Infrasonic Stethoscope for Monitoring Physiological Processes

ABSTRACT

An infrasonic stethoscope for monitoring physiological processes of a patient includes a microphone capable of detecting acoustic signals in the audible frequency bandwidth and in the infrasonic bandwidth (0.03 to 1000 Hertz), a body coupler attached to the body at a first opening in the microphone, a flexible tube attached to the body at a second opening in the microphone, and an earpiece attached to the flexible tube. The body coupler is capable of engagement with a patient to transmit sounds from the person, to the microphone and then to the earpiece.

CROSS-REFERENCE TO RELATED PATENT APPLICATION(S)

This application claims the benefit of and priority to U.S. ProvisionalApplication Ser. No. 62/058,794, filed on Oct. 2, 2014, the contents ofwhich are incorporated by reference herein in their entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

The invention described herein was made in the performance of work undera NASA contract and by employees of the United States Government and issubject to the provisions of Public Law 96-517 (35 U.S. C. §202) and maybe manufactured and used by or for the Government for governmentalpurposes without the payment of any royalties thereon or therefore. Inaccordance with 35 U.S. C. §202, the contractor elected not to retaintitle.

FIELD OF THE INVENTION

The present disclosure relates to an infrasonic stethoscope (or“infrascope”) for monitoring physiological processes and is particularlyrelated to a wireless infrasonic stethoscope.

BACKGROUND OF THE INVENTION

Sound at frequencies below 20 Hertz is termed “infrasound.” Aparticularly favorable property of infrasound is its propagation overlong distances with little attenuation. Infrasound has this propertybecause atmospheric absorption is practically negligible at infrasonicfrequencies, and because there is an acoustic “ceiling” in thestratosphere where a positive gradient of the speed of sound versusaltitude causes reflections of infrasonic rays back to Earth. Infrasoundpropagation over long distances (e.g., thousands of kilometers) ispredominantly due to refractive ducting from the upper layers in theatmosphere, while propagation over short distances is completed bydirect path.

The density, acoustic impedance, and speed of sound through differenthuman and animal tissues varies depending upon location of theauscultation. When an acoustic signal travels through tissue layers, theamplitude of the original signal becomes more attenuated with depth ofthe acoustic signal source. Attenuation (i.e. energy loss) could be dueto absorption, reflection, and scattering at interfaces of differenttissues. The degree of attenuation also depend upon frequency of thesound wave and the distance it travels. Generally speaking, a highfrequency acoustic signal is associated with high attenuation thuslimiting tissue penetration, but lower frequencies do not haveattenuation issue thus providing physicians better understanding of theheart performance. More than 60% power spectral density of heart signalsfall in infrasonic bandwidth. Low frequency acoustic signals detectedfrom different human organs, such as the heart, are valuable tophysicians for monitoring heart and lungs.

Microphones and stethoscopes are regularly used by physicians indetecting sounds for monitoring physiological conditions.Phonocardiography has been in use for more than 75 years to monitorheart beats as well as to detect the audible sound of the blood flowingthrough the heart. These physiological condition monitors are coupleddirectly to a person's body and processes are measured either bylistening or by recording the signals in certain bandwidth. Thephysiological processes such as respiration and cardiac activity arereflected in a different frequency bandwidth from 1/10 Hertz to 500Hertz. Other stethoscopes are capable of monitoring only audiblefrequency bandwidth, and are not capable of monitoring infrasonicfrequencies below 20 Hz. Low frequency acoustic signals below 20 Hertzare not audible, but can provide useful information to physicians.

Inside of a normal heart, there are four chambers namely; the rightatrium, the left atrium, the right ventricle, and the left ventricle.The function of a heart is to keep blood flowing in one-way direction.When a valve opens, the valve lets the right amount of blood through,and then closes to keep blood from flowing backwards in between beats.An easy and relatively inexpensive assessment of any patient's cardiacstatus can be determined by sounds in the chest. The key to goodauscultation lies in low and high pitched sounds. As the heart beats,blood flows from right atrium into the right ventricle through thetricuspid valve.

Blood then flows to the lungs through pulmonary valve (sometimes alsocalled semilunar valve) to pick up right amount of oxygen. The bloodflows from the lungs back into the left atrium and enters into the leftventricle through the mitral valve. Blood then is pumped to the aortathrough the aortic valve and goes out to rest of the body providingoxygen and nutrients to the body cells. All four chambers (right atrium,right ventricle, left atrium, and left ventricle) must contract at justthe right time for normal heart to functioning properly. The propertiming is coordinated by heart's electrical pathways. The electricalsignals are produced by the sinoatrial node (SA node) andatrioventricular node (AV node).

The SA node is a group of cells located in the right atrium thatinitiates contraction of both atria to push blood into theircorresponding ventricles. Due to insulation between the atria andventricles, the SA node signals do not continue directly to theventricles but pass through the AV node, which is another group of cellslocated in the floor of right atrium between the atria and ventricles.The AV node regulates the signal to ensure that the atria are empty andclosed before the ventricles contract to push the blood out of theheart. The SA node sends signals to stimulate the heart to beat between60-100 times per minute.

The cardiovascular system is complex and numerous problems could takeplace inside anywhere from the electrical system of the heart to thelarge or small blood vessels. There are over 60 different types ofcardiovascular disease, all of which somehow affect the cardio orvascular systems. The heart sounds generated by the beating of heart andthe resultant flow of blood can provide important information about thecondition of the heart. In healthy adults, two normal heart sounds occurin sequence with the heartbeat. A first sound is produced based on theclosure of the atrioventricular valves (i.e. mitral and tricuspidvalves) located between the atria and ventricles, and is referred to asS1. A second sound is produced as a result of closure of the semilunarvalves (i.e. pulmonary and aortic valves), which control the flow ofblood as it leaves the heart via the arteries, and is referred to as S2.

The first heart sound S1 consists of four sequential components: 1.Small low frequency vibrations that coincide with the beginning of leftventricular contraction. 2. High frequency vibration, easily audiblerelated to mitral valve closure (M1). 3. A second high frequencycomponent related to tricuspid valve closure. 4. Small frequencyvibrations that coincide with the acceleration of blood into greatvessel.

In addition to these normal sounds, a variety of other sounds may bepresent but requires highly sensitive microphone with lowest acousticbackground noise level along with filters to pick up these sounds. Athird low frequency sound, which may be heard at the beginning of thediastole, is referred to as S3. A fourth sound may be heard in latediastole during atrial contraction, is referred to as S4. These soundscan be associated with heart murmurs, adventitious sound, ventriculargallop and gallop rhythms. The S4 provides information abouthypertension and acute myocardial infarction.

The cardiac sounds S1, S2, S3, and S4 can be attributed to specificcardiac activity. S1 is attributed to the onset of the ventricularcontraction (10-140 Hertz bands). S2 is attributed to closure of thesemilunar valves (10-400 Hertz bands). S3 may be attributed toventricular gallop, which may be heard during rapid filling (i.e.diastole) of the ventricles. S4 may be attributed to atrial gallop,which may be heard in late diastole, during atrial contraction. S3 andS4 are of very low intensity and can be heard externally when amplified.

Other sounds may be heard from opening snaps of the mitral valve orejection sound of the blood in the aorta which indicates valvemalfunctions, such as stenosis or regurgitation. Other high frequencymurmurs can occur between the two major heart sounds during systole ordiastole. The murmurs can be innocent but can also indicate certaincardiovascular defects.

Continuous fetal heart monitoring is an important step to evaluate thewell-being of a fetus. The fetal heart rate may indicate if the fetus isgetting enough oxygen. Most of the time ultrasound transducers are usedfor monitoring fetal heart rate as conventional stethoscopes undesirablypick up signals from maternal abdominal vessels. Due to abdominal fat ofthe mother or fetal positioning, it may be difficult to monitor fetalheart passively, so most of the time ultrasound transducers are usedwhere ultrasound pulses are radiated towards the fetus and reflectivepulses are used for monitoring. If enough reflective signals are notreceived, the penetration depth of ultrasound pulses are increased whichmay decrease quality and signal-to-noise ratio. The high frequencyultrasound signals become attenuated due to absorption, reflection, andscattering due to abdominal fat. The infrasound signals have relativelyvery low attenuation coefficient hence the signals are expected to be ofhigh quality with better signal to noise ratio and helpful togynecologists.

Many heart sounds are in a low-frequency band spectrum with lowintensity level and may require extremely sensitive infrasonicmicrophone to acquire useful information that cannot be perceived by thephysician's ear. The passive filtering may be useful to record low andhigh frequency bands separately. The sounds are of short duration andhighly non-stationary but enable to measuring systolic and diastolictime intervals, which may have diagnostic importance.

Accordingly, there is a need for a monitoring device that overcomes thedisadvantages presented by the prior art.

BRIEF SUMMARY OF THE INVENTION

An infrasonic stethoscope (or infrascope) or monitoring physiologicalprocesses of a patient includes a microphone capable of detectingacoustic signals in the audible frequency bandwidth and in theinfrasonic bandwidth. The microphone has a body, which includes firstand second spaced apart openings. A body coupler is attached to thefirst opening of the body to form a substantially air-tight seal,wherein the body coupler is capable of engagement with the patient tomonitor physiological processes. A flexible tube is attached to the bodyat the second opening in the microphone. An earpiece is attached to theflexible tube. The body coupler is capable of engagement with a patientto transmit sounds from the patient to the microphone, and then to theearpiece.

These and other features, advantages, and objects of the presentinvention will be further understood and appreciated by those skilled inthe art by reference to the following specification, claims, andappended drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The organization and manner of the structure and operation of thedisclosed embodiments, together with further objects and advantagesthereof, may best be understood by reference to the followingdescription, taken in connection with the accompanying drawings, whichare not necessarily drawn to scale, wherein like reference numeralsidentify like elements in which:

FIG. 1 is perspective view of an embodiment of an infrascope which canbe used for external monitoring of a patient;

FIG. 2 is a perspective view of the infrascope attached to a catheter,for use in internal fetal monitoring of a patient;

FIG. 3 is a perspective view of a pair of infrascopes which can be usedin Doppler phonocardiography;

FIG. 4 is a graph showing bandwidths of heart sound;

FIG. 5 is a cross-sectional view of a microphone which forms part of aninfrascope of the present invention and of a body coupler according to afirst embodiment attached to the microphone and which forms part of theinfrascope of the present disclosure;

FIG. 5A is a cross-sectional view of a body coupler according to asecond embodiment and which forms part of the infrascope of the presentdisclosure;

FIG. 6 is a schematic view of a skeleton of a patient;

FIG. 7 is a flow chart regarding the process of how signals from theinfrascope are transmitted and analyzed;

FIGS. 8-17 are charts of infrascope signals collected at locations A, P,T and M of FIG. 6 with reference to electrocardiogram signals referredas ECG or EKG; and

FIGS. 18 and 19 show charts of infrascope data as compared to ECG or EKGon two different subjects from 1 Hz through 1000 Hz.

DETAILED DESCRIPTION OF THE INVENTION

While the disclosure may be susceptible to embodiment in differentforms, there is shown in the drawings, and herein will be described indetail, a specific embodiment with the understanding that the presentdisclosure is to be considered an exemplification of the principles ofthe disclosure, and is not intended to limit the disclosure to that asillustrated and described herein. Therefore, unless otherwise noted,features disclosed herein may be combined together to form additionalcombinations that were not otherwise shown for purposes of brevity. Itwill be further appreciated that in some embodiments, one or moreelements illustrated by way of example in a drawing(s) may be eliminatedand/or substituted with alternative elements within the scope of thedisclosure.

As shown in FIG. 1, an infrascope 20 is provided to monitorphysiological processes of a patient. The infrascope 20 detects signalsin a bandwidth from 0.03 Hertz through 1000 Hertz, or alternatively 0.03through 500 Hertz. These bandwidths contains signals which are audibleand inaudible to the human ear. The infrascope 20 has multipleapplications to measure a variety of human physiological processes,including, but not limited to, cardiac monitoring, external fetalmonitoring, internal fetal monitoring, stress phonocardiography testing,Doppler phonocardiography, biometric identification and polygraphs. Thebandwidth of audible and inaudible sounds produced by cardiac activityare shown in FIG. 4, which demonstrates energy distribution (dynes/cm²)as a function of frequency (Hz).

The infrascope 20 contains a microphone 22, a body coupler 24 or 24 aattached to the microphone 22, a flexible tube 26 attached to themicrophone 22 and earpiece 28 connected to the flexible tube 26. Forinternal fetal monitoring, as shown in FIG. 2 and as further describedherein, the body coupler 24 a is used and the microphone 22 is furtherconnected to a catheter 23 via the body coupler 24 a.

The microphone 22 is substantially the same as the microphone describedin U.S. Pat. No. 8,401,217, with the modifications described herein. Thecontents of U.S. Pat. No. 8,401,217 is incorporated by reference in itsentirety.

The microphone 22 is best shown in FIG. 5 and includes a cup-like body30, a cup-like support plate 32, an insulating member 34, a conductor36, a backplate 38, a membrane 40 and a low-noise preamplifier board 42.

The body 30 has a cylindrical side wall 44 having a proximal end and adistal end, an end wall 46 at the proximal end of the body 30, and aconnection port 48 extending proximally from the end wall 46. The body30 is formed of metal, such as a stainless steel or aluminum. The sidewall 44 and the end wall 46 define an internal cavity 50 within the body30. The distal end of the body 30 is open such that an aperture 52 isdefined in the body 30. A thread form 54 is provided on the exteriorsurface of the side wall 44 at the distal end. The end wall 46substantially closes the proximal end of the body 30, with the exceptionof an aperture 56 therethrough, and may extend perpendicularly relativeto the side wall 44. The aperture 56 may be centrally located in the endwall 46 and is communication with the connection port 48. The connectionport 48 extends proximally from the end wall 46 and has a passageway 58therethrough which is communication with the cavity 50 via the aperture56. The exterior surface of the connection port 48 has a thread form 60thereon. An aperture 62 is provided through the side wall 44 at aposition spaced from the proximal end of the side wall 44.

The support plate 32 is attached to the internal surface of the sidewall 44 and seats within the cavity 50. The support plate 32 is formedof metal, and has a circular base wall 64 which spans the diameter ofthe side wall 44 and is parallel to the end wall 46, and a dependingside wall 66 which extends distally from the base wall 64. The side wall66 terminates in a free end. The side wall 66 engages against theinternal surface of the side wall 44 of the body 30, such that the freeend of the side wall 66 is proximate to the distal end of the body 30,and the base wall 64 is spaced from the distal end of the body 30. Thesupport plate 32 is affixed to the body 30 by suitable means, such aswelding, in such a way that whole assembly can be connected to theground of preamplifier board 42. As a result of this arrangement, adistal chamber 68 is formed between the base wall 64 and the distal endof the body 30, and a proximal chamber 70 is formed between the basewall 64 and the proximal end of the body 30. The base wall 64 has anaperture 72 therethrough, which may be centrally located. The base wall64 also has at least one aperture 74 or slot therethrough to allow airto flow from the distal chamber 68 to the proximal chamber 70.

The insulating member 34, which may be formed of plastic, ceramic, woodor any suitable insulating material, seats within the aperture 72 in thesupport plate 32 and is used to electrically isolate the conductor 36,the backplate 38 and the preamplifier board 42 from the support plate32. As shown, the insulating member 34 has a central portion 76 whichextends through the aperture 72, a proximal portion 78 which extendsradially outwardly from the central portion 76 on the distal side of thebase wall 64, and a distal portion 80 which extends radially outwardlyfrom the central portion 76 on the proximal side of the base wall 64. Apassageway 82 extends through the central portion 76.

The backplate 38 is formed of a conducting material, and is formed froma base wall 88 and may further be formed of a proximal extending portion90 which extends perpendicularly from the base wall 88. The backplate 38may be formed of, for example, from conducting ceramics, brass, orstainless steel. A passageway 89 extends through the base wall 88, andextending portion 90 if provided, from its proximal surface to itsdistal surface. A permanently polarized thin polymer film 91 is coatedon the distal surface of the backplate 38. The polarized thin polymerfilm 91 operates without the need for an external power supply. Asdescribed in U.S. Pat. No. 8,401,217, the backplate 38 has a pluralityof spaced apart holes 92 therethrough (two holes are visible in FIG. 5.The extending portion 90 engages against the distal portion 80 of theinsulating member 34, and is secured to a distal end of the conductor36, such that the backplate 38 and the conductor 36 are in electricalcommunication. The base wall 88 of the backplate 38 is parallel to thebase wall 64 of the support plate 32. A slot 94 is defined between theouter diameter of the backplate 38 and the side wall 44 of the body 30.The area between the backplate 38 and the proximal end of the body 30defines a backchamber.

The conductor 36 extends through the passageways 82, 89 and extends intothe proximal chamber 70. The conductor 36 is electrically connected tobackplate 38. As shown, the conductor 36 is formed of a conducting rodor wire 84 which extends through the passageways 82, 89, and aconductive rod 86 extending proximally from the conducting rod or wire84 and the insulating member 34. If formed of two components, thecomponents are suitably connected to each other to form an electricalconnection. The rod or wire 84 and rod 86 may be formed of brass, or maybe formed of differing conductive materials. The proximal end of theconductor 46 is proximate, to but spaced from, the end wall 46 such thata gap is defined therebetween.

The membrane 40 is formed of a flexible conductive material and isseated at the distal free end of the side wall 66 of the support plate32 such that the membrane 40 is positioned within the distal chamber 68and is proximate to, but spaced from, the distal end of the body 30. Thediameter of the membrane 40 is selected so that the membrane 40 stayswithin side wall 66. The membrane 40 is parallel to the end wall 46 ofthe body 30 and to the base wall 64 of the support plate 32. As aresult, the membrane 40 is in electrical communication with the supportplate 32. The tension of the membrane 40 may be less than about 400Newton per meter.

The backplate 38 is proximate to, but spaced from the membrane 40, suchthat an air gap 98 is formed between the membrane 40 and the backplate38 to create a capacitor in the microphone 22 as is described in U.S.Pat. No. 8,401,217. As described in U.S. Pat. No. 8,401,217, the number,locations and sizes of the holes 92, the size of the slot 94, and theinner volume of the backchamber are selected such to allow enough airflow to provide proper damping of the motion of the membrane 40. Asdescribed in U.S. Pat. No. 8,401,217, the backchamber serves as areservoir for the airflow through the holes 92 in the backplate.

In an exemplary embodiment, the membrane 40 has a diameter ofapproximately 1.05 inches (0.0268 meter). The membrane 40 may have thefollowing characteristics/dimensions:

-   -   radius=0.0134 meter;    -   thickness=2.54×10⁻⁵ meter;    -   density=8000 kilogram/meter³;    -   tension=400 N/meter;    -   surface density=0.1780 kilogram/meter²; and    -   stress=47.4045 PSI.        The microphone 22 may comprises an air layer which may have the        following characteristics/dimensions:    -   air gap=2.54×10⁻⁵ meter;    -   density=1.2050 kilogram/meter³;    -   viscosity=1.8×10⁻⁵ Pascal-second;    -   sound velocity through the air gap=290.2 meters per second; and    -   gamma=1.4        The microphone 22 may also comprise a slot 94 which may have the        following characteristics/dimensions:    -   distance from the center of the backplate=0.0117 meter;    -   width=0.00351 meter;    -   depth=0.00114 meter; and    -   area=0.000258 meter².        The backplate 38 may define six holes 92, and each hole 92 may        have the following characteristics/dimensions:    -   distance from center of backplate to center of hole=0.00526        meter;    -   radius=0.002 meter;    -   depth=0.045 meter;    -   angle between two lines going from center of backplate to either        side edge of hole=43.5 degrees; and    -   area=1.26×10⁻⁵ meter².        The microphone 22 may also have the following further        characteristics/dimensions:    -   volume of the backchamber=5×10⁻⁵ meter³;    -   membrane mass=480 kilogram/meter⁴;    -   membrane compliance=3.2×10⁻¹¹ meter⁵/Newton; and    -   air gap compliance=3.5×10⁻¹⁰ meter⁵/Newton.

In one embodiment, the resonant frequency of the microphone 22 may be3108.01 Hertz.

The preamplifier board 42 is planar and extends radially outwardly fromthe proximal end of the conductor 36. The preamplifier board 42 isconnected to the proximal end of the conductor 36 by suitable means suchthat there is an electrical connection between the preamplifier board 42and the conductor 36, such as a brass screw 99. The preamplifier board42 is parallel to the end wall 36 of the body 30, the base wall 64 ofthe support plate 32 and the base wall 88 of the backplate 38. Theposition of the preamplifier board 42 defines a first proximal chamber100 which has a volume V1 between the preamplifier board 42 and the endwall 46 of the body 30, and a second distal chamber 102 which has avolume V2 between the preamplifier board 42 and the base wall 64 of thesupport plate 32. A slot 104 is defined between the outer diameter ofthe preamplifier board 42 and the side wall 44 of the body 30 to allowair to flow from the distal chamber 102 to the proximal chamber 100. Inan embodiment, volume V1 is approximately 0.1287 cubic inch, and volumeV2 is approximately 0.6 cubic inch. The air can only flow from thedistal chamber 102 to the proximal chamber 100 through the slot 104. Inan embodiment, this slot 104 has a clearance distance between the outerdiameter of the preamplifier board 42 and the side wall 44 ofapproximately 0.025″, which slot 104 extends around the preamplifierboard 42.

An electrical connection 106 extends through the aperture 62 in the sidewall 44 and is sealed to the side wall 44 by suitable means. Theelectrical connection 106 is electrical communication with thepreamplifier board 42 via wires 108, 110. The preamplifier board 42 isalso electrically connected to the body 30 via a wire 110, whichprovides a ground to the preamplifier board 42. The preamplifier board42 contains known components for measuring the capacitance between themembrane 40 and the backplate 38, and converting this measuredcapacitance into voltage.

The connection port 48 is connected to a distal end of the flexible tube26, which may be formed of latex or rubber, which has an earpiece 28 atthe proximal end of the tube 26. Such a flexible tube 26 and earpiece28, like a typical stethoscope, are known in art for transmitting sound.The flexible tube 26 is attached to the connection port 48, such thatthere is no air exchange between the flexible tube 26 and the body 30,and such that the passageway through the tube 26 is in communicationwith the distal chamber 100 via the passageway 58 and aperture 56. Whenthe earpiece 28 is inserted into the ears of the medical personnel, thisallows substantially no air exchange between the cavity 50 of themicrophone 22 and the outside the microphone 22. The length of theflexible tube 26 is adjusted so that maximum audible sound is receivedat the earpiece 28, which are used by medical personnel to hear thedesired sounds in real time.

The combination of volumes V1 and V2 and the slot 104 around thepreamplifier board 42 provide sufficient acoustic resistance forpressure equalization, and lowers the low frequency threshold. When theflexible tube 26 is connected to the earpiece 28, due to increasedacoustic resistance and longer required period for pressureequalization, this lowers the low −3 dB frequency to 0.03 Hertz.

As described herein, the microphone may differ from U.S. Pat. No.8,401,217 in that the body 30 is not completely sealed in that aconnection port 48 is provided for connecting the microphone 22 to theflexible tube 26 and the earpiece 28, in that the preamplifier board 42is mounted horizontally in the body 30 to divide the backchamber intotwo lower chambers 100 and 102 and that the preamplifier board 42 isparallel to the membrane 40, rather than being positioned verticallythat is perpendicular to the membrane 40 as is positioned in U.S. Pat.No. 8,401,217, and in that the grid of U.S. Pat. No. 8,401,217 iseliminated and instead body 30 includes threads 54 for connection of thebody coupler 24 or 24 a to the distal end of the body 30.

The body coupler 24, 24 a threadedly attaches to the thread form 54 atthe distal end of the body 30 such that there is no air exchange betweenthe body coupler 24, 24 a and the body 30. In one embodiment, as shownin FIG. 5, the body coupler 24 is formed of an outer ring 114 which hasa flexible non-conductive diaphragm 116 attached thereto and which spansthe diameter of the ring 114. The outer ring 114 may be formed either ofthermoplastic polyurethane elastomers (TPU) or of closed cellpolyurethane foam material which can be made of different densities, andhas an internal thread form 118 for attachment of the outer ring 114 tothe distal end of the body 30. The TPU material is used when fullspectrum of acoustic signals are to be recorded from a heart and closedcell polyurethane foam material is used only when infrasonic signals isto be recorded as this material acts as a passive filter and audiblesound is shunted off. When attached, the membrane 40 of the microphone22 and the diaphragm 116 of the body coupler is approximately 0.1 inchapart. The body coupler 24 is placed against the body of the patientduring the monitoring of the physiological process. In anotherembodiment, as shown in FIG. 5A, the body coupler 24 a has a cup-likewall 120 having opposite proximal and distal ends and which defines acavity 126 therein, and a connection port 122 extending from the distalend. The connection port 122 has a passageway 128 therethrough which isin fluid communication with the cavity 126 by an aperture 130 throughthe wall 120. The exterior surface of the connection port 122 may have athread form thereon. The proximal end of the wall 120 is open and athread form 124 is provided on the interior surface of the wall 120. Thewall 120 and connection port 122 are formed either of aluminum or brass.With this second embodiment of the body coupler 24 a, the proximal endof the flexible catheter tube 23 is attached to the connection port 122,and the thread form 124 engages with the thread form 54 on the body 30of the microphone 22. As such, the connection between the catheter tube23, the body coupler 24 a and the microphone 22 is sealed to prevent airentrance therethrough. As is known, catheter tubes 23 have opening(s) 25at the end of the tube 23. The end of the tube 23 may be inserted intothe bladder 132 of a patient to provide internal fetal monitoring. Thebladder 132 is proximate to the uterus 134 and sound, specificallyinfrasound, transmission is conveyed from the uterus 134, to the bladder132, to the catheter tube 23 via the opening(s) 25, and then to themicrophone 22.

As discussed herein, the preamplifier board 42 is installed parallel tothe base wall 54 and to the membrane 24. The slot 104 between the edgeof the preamplifier board 42 and the side wall 44 is small, for example0.025″, to increase acoustic resistance. The combined volumes V1 and V2and the volume in the flexible tube 26 is 5×10−5 meter³. Because ofincreased acoustic resistance, pressure equalization takes longer whichaids in lower −3 dB frequency to 0.03 Hertz.

In use, the body coupler 24 or catheter tube 23 detects incident soundpressure from the heart, the uterus, or from any other location of thebody where it is placed. For example as shown in FIG. 6, the bodycoupler(s) 24 may be placed at locations A, P, T and/or M on the body ofthe patient. The sound pressure excites the motion of the membrane 40within the microphone 22. The motion of the membrane 40 changes thecapacitance between the membrane 40 and the backplate 38. Thiselectrical signal travels from the backplate 38, through the conductor36 and to the preamplifier board 42, thereby producing a proportionaloutput voltage at the preamplifier board 42. The preamplifier board 42is grounded via wire 112. The signal is sent from the preamplifier board42 through the sealed electrical connection 106 to an electronics boardwhich digitizes and transfers the data wirelessly to a nearby computer.The received signals are detected in the bandwidth of 0.03 through 1000Hertz.

The microphone 22 provides damping of the motion of the membrane 40 forflat frequency response over a desired range by using the air gap 98 andthe holes 92 in the backplate 38. When the membrane 40 vibrates, themembrane 40 compresses and expands the air layer in the air gap 98 andcreates a reaction pressure, which opposes the motion of the membrane40. The reaction pressure generates airflow which introduces dampingprimarily at two places: in the air gap 98 between the membrane 40 andthe backplate 38, and in the holes 92 in the backplate 38 which providelarge surface areas for viscous boundary layer damping.

As described in U.S. Pat. No. 8,401,217, in a 3 inch diameter infrasonicmicrophone 22, the tension of the membrane 40 may be less than about1500 Newton per meter. For example, where the radius of the membrane 40is about 0.0342 meter, the tension of the membrane 40 may be less thanabout 1000 Newton per meter. Further, the resonance frequency of themicrophone 22 may be less than about 1000 Hertz. Still further, thevolume of the backchamber may be selected to produce a low-frequency aircompliance that exceeds the compliance of the membrane 40 by a factor ofat least 3. In one example, the radius of the membrane 40 is about0.0342 meter. In this example, the backplate 38 defines six holes 92,each having a radius of about 0.00302 meter. The holes 92 are evenlyspaced along an imaginary circle on the backplate 38 and a center ofeach hole 92 is aligned with the imaginary circle. The center of theimaginary circle is located coincident with a center of the backplate38, and the radius of the imaginary circle is about 0.0105 meter. Thewidth of the slot 94 is about 0.0144 meter and the area of the slot 94is about 0.00179 m².

In an approximately 1.5 inch diameter infrasonic microphone 22, wherethe radius of the membrane 40 is about 0.0134 meter, the tension of themembrane 40 may be less than about 400 Newton per meter. Further, theresonance frequency of the microphone 22 may be less than about 1500Hertz. Still further, the volume of the backchamber may be selected toproduce a low-frequency air compliance that exceeds the compliance ofthe membrane 40 by a factor of at least 10. In another example, theradius of the membrane 40 is about 0.0134 meter. In this example, theradius of each of the six holes 92 is about 0.002 meter and the radiusof the imaginary circle is about 0.0117 meter. The width of the slot 94is about 0.00351 meter and the area of the slot 94 is about 0.000258 m².The volume of the backchamber is about 0.00005 m³.

As shown in the block diagram of FIG. 7, the signals from the infrascope20 are digitized via an analog to digital digitizer board 140. Oncedigitized, the signal is transmitted wirelessly or by cable toworkstation 142, such as a laptop or personal computer. At 144, timehistory is plotted for data collected at different locations of thepatient such as at locations A, T, P and M as shown in FIG. 6. Theworkstation 142 provides control, analysis and display of the recordeddata. MATLAB may also be used to process the data to generate thereal-time spectrograms using short-time Fourier transform (STFT)spectrum of the corresponding data at 146 and 148. The time history andspectrogram of biological signals is transferred by the Internet 150 toa remote workstation 152, if desired, for observation and analysis.Examples of such remote workstations 52 may be a remote computermonitor, smartphone or tablet. The signals may be sent via wiredconnection, or may be wirelessly transmitted, such as by usingcommercially available Bluetooth module, to PC or laptop for processing.The data is converted in useful visual format also called spectrogram,which may be helpful for physician to diagnose any abnormality. Thedisplay of short term spectra is performed in real time, in order todetect the presence of a short term event in the data.

FIGS. 8-17 show charts of infrascope signals collected at locations A,P, T and M of FIG. 6 with reference to electrocardiogram signals usuallyreferred as ECG or EKG. FIGS. 18 and 19 show charts of infrascope dataas compared to ECG or EKG on two different subjects from 1 Hz through1000 Hz. The ECG signals of both subjects are quite different andinfrascope signals also follow the trend of ECG.

The infrascope 20 can be used for a stress phonocardiography test. Someheart problems occur only during physical activity. Stressphonocardiography test can be accomplished using the signals from theinfrascope 20 immediately before and after walking on a treadmill orriding a stationary bike.

The infrascope 20 may be used for fetal heart monitoring duringpregnancy, labor, and delivery to keep track of the heart rate of afetus and the strength and duration of the contractions of uterus.External fetal heart monitoring which involves placing the body coupler24 against the abdomen of the patient, keeps track of the baby's heartrate while at rest and while moving; measures the number of contractionsand how long contractions last during labor and delivery; determines ifthere is preterm labor. Internal fetal heart monitoring, as shown inFIG. 2 and which uses the catheter 23 as described herein, determines ifthe stress of labor is threatening the baby's health; measures thestrength and duration of the labor contraction.

The infrascope 20 can be used for Doppler phonocardiography as shown inFIG. 3. A Doppler phonocardiography can be used to measure blood flowwithin the heart without an invasive procedure. The left ventricularfilling pressure and blood flow can be estimated by using twoinfrascopes 20. The infrascopes 20 can be placed at any desiredlocation, for example locations A, P, T and M, by using a mountingstructure 160 having adjustable rods 162 attached to the microphones 22to determine two dimensional velocity estimation and imaging.

The infrascope 20 can be used for biometric identification. Fingerprintshave been used for identification for more than 100 years, but usingheartbeat for biometric identification has some advantages such asconvenience and security. The heartbeat signatures can be extractedusing either ECG/EKG or by using the infrascope 20 at remote locations.The security feature is preserved from the fact that a user's ECG oracoustic signatures cannot be captured without a person's consent.Another disadvantage of fingerprints are that these can be replicated byusing samples left behind. The infrasonic bandwidth signals providebetter and higher signal to noise ratio values and another tool forbiometric identification.

The infrascope 20 can be used for polygraphs. Physiological processesmeasured by polygraphs are; cardiovascular, electrodermal, andrespiratory. The direction and extent of cardiovascular reactivity maybe different across individuals in response to stimuli that may beconsidered arousing. Electrodermal activity in terms of skin resistanceor conductance is measured by passing a current through the skin. Inresponse to controlled and relevant questions, variations from basallevels are called electrodermal or EDR responses or electrodermalactivity levels and is used for polygraph interpretation. Variations inrespiration which also produce changes in heart rate and electrodermalactivity is monitored to determine of responses to relevant and controlquestions are artifacts. Currently, the rate and depth of respirationduring polygraph are measured by changes measured using strain gaugespositioned on chest and abdomen. Extreme low frequency signalmeasurements can be made by positioning the infrascope 20 at a subject'schest and abdomen is a relatively inexpensive tool to measure variationin respiratory and cardiovascular activity.

The infrascope 20 of the present disclosure enables medical personnel tolook at the audible bandwidth as well as infrasonic bandwidth, thusproviding medical personnel with another tool to analyze physiologicalprocesses. The infrascope 20 can be used for respiratory, cardiac, andfor fetal heart monitoring. The infrascope 20 enables physiologicalprocess signals to be transferred to any place in the world in realtime. Ambulances can be equipped with the infrascope 20 and medicalpersonnel are able to obtain a patient's physiological information inreal time. The infrascope 20 is a relatively inexpensive tool todiagnose abnormality at early stage.

The terms “patient” is used throughout the disclosure, which includeshumans and animals, as it is anticipated that the present inventionwould also be capable of monitoring physiological processes forveterinary practices.

All references disclosed herein are hereby incorporated by reference intheir entirety.

While particular embodiments are illustrated in and described withrespect to the drawings, it is envisioned that those skilled in the artmay devise various modifications without departing from the spirit andscope of the appended claims. It will therefore be appreciated that thescope of the disclosure and the appended claims is not limited to thespecific embodiments illustrated in and discussed with respect to thedrawings and that modifications and other embodiments are intended to beincluded within the scope of the disclosure and appended drawings.Moreover, although the foregoing descriptions and the associateddrawings describe example embodiments in the context of certain examplecombinations of elements and/or functions, it should be appreciated thatdifferent combinations of elements and/or functions may be provided byalternative embodiments without departing from the scope of thedisclosure and the appended claims.

What is claimed is:
 1. An infrasonic stethoscope for monitoringphysiological processes of a patient, comprising: a microphone capableof detecting acoustic signals in a frequency range of 0.03 Hertz to 1000Hertz, the microphone comprising a body having first and second spacedapart openings; a body coupler attached to the first opening of the bodyto form a substantially air-tight seal, wherein the body coupler iscapable of engagement with the patient; a flexible tube attached to thebody at the second opening; and an earpiece attached to the flexibletube.
 2. The infrasonic stethoscope of claim 1, wherein the body forms acavity, and further comprising a conductive backplate within the cavityand defining a backchamber between the backplate and the body, aconductive membrane within the cavity, the backplate and the membranespaced apart from each other to form a capacitor, and further includinga preamplifier board in electrical connection with the backplate, thepreamplifier capable of measuring the capacitance between the membraneand the backplate and converting this measured capacitance into voltage.3. The infrasonic stethoscope of claim 2, wherein the preamplifierboard, the backplate and the membrane are parallel to each other.
 4. Theinfrasonic stethoscope of claim 2, wherein the backplate defines aplurality of holes, wherein a slot is defined between an outer diameterof the backplate and an inner wall of the body, and wherein locationsand sizes of the holes and a size of the slot are selected such thatmembrane motion is substantially critically damped.
 5. The infrasonicstethoscope of claim 2, further comprising a conductive support platemounted to said body, the support plate having a passageway and at leastone aperture therethrough; an insulating member extending through thepassageway in said support plate; a conductive member extending throughthe insulating member and extending therefrom, the conductive member iselectrically connected to the backplate and to the preamplifier board,wherein the backplate is on one side of the support plate and thepreamplifier board is on an opposite side of the support plate.
 6. Theinfrasonic stethoscope of claim 5, wherein the backplate is seated onthe insulating member.
 7. The infrasonic stethoscope of claim 2, whereina slot is defined between the preamplifier board and the body having alength of approximately 0.025″.
 8. The infrasonic stethoscope of claim7, wherein the preamplifier board defines a first chamber in the bodyhaving a volume of approximately 0.1287 cubic inch, and a second chamberin the body having a volume of approximately 0.6 cubic inch.
 9. Theinfrasonic stethoscope of claim 2, wherein the preamplifier boarddefines a first chamber in the body having a volume of approximately0.1287 cubic inch, and a second chamber in the body having a volume ofapproximately 0.6 cubic inch.
 10. The infrasonic stethoscope of claim 2,further comprising a digitizer board which is remote from themicrophone.
 11. The infrasonic stethoscope of claim 2, wherein thesignals from the preamplifier board are digitized and electronicallytransmitted to a remote location.
 12. The infrasonic stethoscope ofclaim 11, wherein the signals of electronically transmitted by wire. 13.The infrasonic stethoscope of claim 11, wherein the signals ofelectronically transmitted wirelessly.
 14. The infrasonic stethoscope ofclaim 1, wherein the body coupler is formed of a ring having a flexible,non-conductive diaphragm attached thereto, and the ring is attached tothe body.
 15. The infrasonic stethoscope of claim 14, wherein the ringand body are threadedly connected.
 16. The infrascope of claim 1,wherein the body coupler is formed of a wall having an outlet port, anda catheter attached to the outlet port.
 17. The infrasonic stethoscopeof claim 1, wherein the body has an outlet port surrounding the secondopening and the flexible tube is threadedly attached to the outlet port.18. The infrasonic stethoscope of claim 1, further comprising adigitizer board which is remote from the microphone.
 19. The infrasonicstethoscope of claim 1, wherein the signals from the preamplifier boardare digitized and electronically transmitted to a remote location. 20.The infrasonic stethoscope of claim 19, wherein the signals areelectronically transmitted in real time.